Pressure stabilizer system



Oct. 18, 1960 c. BOLING 2,956,419

PRESSURE STABILIZER' SYSTEM Filed Nov. 23, 1955 3 Sheets-Sheet 1 'TTETl.

XNVENTOR ATTORN Oct. 18, 1960 c. BOLING PRESSURE STABILIZER SYSTEM 3Sheets-Sheet 2 Filed Nov. 23, 1955 NVENTOB Cec I; Z ,5 o 61/21 r- I mMom W W ATTORNE Oct. 18, 1960 c. BOLING PRESSURE STABILIZER SYSTEM 3Sheets-Sheet 3 Filed Nov. 23, 1955 INVENTOR Cecil flow in WWW? I ATTORNEUnited States Patent PRESSURE STABILIZER SYSTEM Cecil Boling, WestHartford, Conn., assignor, by mesne assignments, to Dunham-Bush, Inc.,West Hartford, Conn, a corporation of Connecticut Filed Nov. 23, 1955,Ser. No. 548,668

9 Claims. (Cl. 62196) This invention relates to refrigeration, and morein particular to maintaining stable operation of refrigeration systemshaving air-cooled condensers throughout Wide variations in thetemperature of the cooling air. The invention also provides formaintaining stable operation of refrigeration systems having other typesof condensers, such as evaporative condensers or condensers used withcooling towers.

It is an object of the present invention to provide improvedrefrigeration systems and modes of operation which overcome diflicultieswhich have been encountered in the past. It is a particular object toprovide a thoroughly practical solution to certain problems caused byunstable operation of refrigeration systems with air-cooled condensersat low ambient temperatures. It is a further object to provide for thesolution of problems which have been encountered with different types ofrefrigeration systems where there is a tendency for overcooling therefrigerant in the condenser during some conditions of operation.

In the refrigeration field, it has become important to provideair-cooled condensers, i.e., which require no cooling water and arecooled by the ambient air only. With such a system, the condenser mustbe of suficient size to give satisfactory performance at peak loads andwith the cooling air at maximum temperature. A refrigeration systemwhich has an air-cooled condenser and which operates to cool a storagecompartment for food or other products or articles must operate withabsolute assurance that the system will not fail because of a rise inthe outside temperature.

Ths is apt to be a particularly serious problem where the system has itscondenser located on the outside of a building and is subjected to veryhigh temperatures during the hot season and very low temperatures duringthe cold season. With such installations, considerable difficulty hasbeen encountered during cold weather because of excessive cooling of theliquid refrigerant in the condenser, i.e., prior to passage to thereceiver. Such excessive cooling causes an objectionably low headpressure; that is, the pressure in the receiver and at the expansionvalve (or restrictor) is reduced to such a low value that therefrigerant does not flow through the expansion valve to the evaporatorat a sufficiently rapid rate. Particularly, the refrigerant pressure inthe receiver is so close to the suction pressure in the evaporator thatthe refrigerant flow is sluggish, and there is insufiicient liquidrefrigerant flow to handle the cooling load. Hence, the evaporator isstarved and is so ineffectual that the refrigerated compartment is notmaintained at the desired low temperature. Under extreme conditions, thehead pressure at the receiver may become so low that the solid column ofliquid refrigerant flowing to the expansion valve may be broken by theformation of gas. In accordance with the present invention, these andrelated difliculties are overcome in a thoroughly practical manner andwith apparatus which is eflicient and dependable m use.

ice

Difficulties similar to those discussed above may be encountered withrefrigeration systems having evaporative condensers or even water-cooledcondensers where the water is cooled in a cooling tower. The presentinvention provides a solution for the above difficulties with variousrefrigeration systems with these other types of condensers.

In the drawings:

Figure 1 is a somewhat schematic representation of one embodiment of theinvention;

Figures 2 and 3 are side and top views respectively of the unit ofFigure 2;

Figure 4 is an enlarged view of the heat interchange unit of therefrigeration system of Figure 1; and,

Figures 5 and 6 are sectional views respectively on the lines 55 and 6-6of Figure 4.

Referring to Figure 1 of the drawings, a motor driven compressor 2discharges hot compressed gas through a line 4, the gas passageway orcircuit of a heat interchange unit 6 and a line 8 to the top of anair-cooled condenser 10. The condensed refrigerant flows from the bottomof the condenser through a line 11, a noranally open valve 12 and a line14 to a receiver 16. The liquid refrigerant flows from the receiverthrough a line 18 having an expansion valve 20 therein to an evaporator22. The gaseous refrigerant is withdrawn from the evaporator through aline 24. Standard control and safety devices are provided.

Extending parallel to valve 12, is a bypass circuit formed by a line 26connected to line 11, the liquid circuit of unit 6 and a line 27connected to line 14. As will be explained more fully below, liquidflowing through this bypass circuit encounters resistance to flow and ispassed in heat interchange relationship with the hot refrigerant gasfrom the compressor.

The details of construction of the heat exchange unit 6 are shown inFigures 2 to 6. Unit 6 has three vertical heat interchange assemblies28, 30, and 32, each formed of a set of three concentric tubes withinternal annular spaces having radial fins therein. These tubeassemblies incorporate certain inventions covered by my prior US.Patents Nos. 2,611,585 and 2,611,587. Assembly 28 is formed (see Figure6) by an outer tube 34, an intermediate tube 36, an inner tube 38, a finassembly 40 positioned in the annular passageway 42 between tubes 34 and36, and a fin assembly 44 similarly positioned in the annular spacebetween tubes 36 and 38. During assembly, tube 36 and its fin assemblyare positioned within tube 34, and then tube 36 is expanded to place thefin assembly under radial compression. Tube 38 and its fin assembly 44are then placed within tube 36, and tube 38 is expanded so as to placethe fin assembly under compression in a similar manner. Fin assembly 40provides a high rate of heat transfer from the gas flowing throughpassageway 42; and, intermediate tube 36 provides the liquid passagewaywith the fin assembly 44 and the inner tube 38 providing the high rateof heat transfer to the liquid flowing therethrough. Assembly 30 issimilarly constructed, with an outer tube 31 and intermediate tube 33,and an inner tube and fin assemblies which are not shown. Assembly 32has an outer tube 41 and intermediate tube 43, and an inner tube and finassemblies (not shown).

The three tube assemblies 28, 30 and 32 are mounted in a pair of headers46 and 48, with the headers open to the annular passageway 42 betweentubes 34 and 36 of assembly 28 and the corresponding passageway of theother assemblies. Hence, these passageways are connected in parallel toprovide three parallel paths for refrigerant gas passing from the inletheaders 46 to the outlet headers 48. The intermediate tubes 36, 33 and43 of the three tube assemblies extend through the head ers, and areconnected in series by a pair of U-tubes 50 and 52. The upper end oftube 43 is connected to tube 26 which acts as the liquid refrigerantinlet line, and the. lower end of tube 36 is connected to tubeor line 27which is the liquid outlet line.

Rigidly mounted in the upper end of the intermediate tube 43 of assembly32 is an orifice ring or perforated disc 54 (see Figure 5) which has acenter opening therethrough which acts as the restricting orifice 56 forthe fiow of liquid refrigerant through the bypass circuit. Hence, liquidmay flow from the upper end of line 11 through line 26 to the upper endof tube 43, through this orifice 56, and thence in series through tubes43, 33 and 36, and from the lower end of tube 36 through line 27 to line14. I

It has been indicated that the orifice 56 provides a fixed resistance toliquid flow, and there is some resistance to flow through the liquidcircuit of unit 6, so that the liquid bypass circuit has designed intoit a predetermined total resistance to liquid flow or restriction.However, the gas circuit has extremely low resistance to gas fiowbecause of the headers and the parallel tube arrangement. At the sametime, the fin assemblies insure that the liquid flowing through thebypass circuit is in intimate heat exchange relationship with the gasflowing through the gas circuit of unit 6 to transfer heat from the hotgas to the liquid refrigerant.

As has been pointed out above, valve 12 is noirnally open, but thisvalve is of the self-closing type, and it closes gradually as thepressure in line 11 drops below a predetermined value. Valve 12 has avalve member 6! which is supported by a bellows 62, and is adapted tomove into the valve o'pening 64 aginst its seat, thus to completelyclose the valve. A compression spring 61 rests against the valve member6%) at the top of the bellows, and the bottom of the spring restsagainst an adjusting unit 63 carrying an adjusting knob 65. By manuallyturning knob 65,'the spring 61 may be compressed more or less so as toadjust the pressure exerted by the spring upwardly on the valve member.The liquid refrigerant pushes downwardly on the top of the valve member,and the spring and atmosphere pressure push upwardly thereon. However,the spring is so adjusted that the differential in pressure above andbelow the valve member holds the valve in its fully open position duringnormal operation of the refrigeration system. That is, when there issufiicient head pressure at line 11 to insure that there will besatisfactory fiow of liquid refrigerant through the expansion valve 20,the refrigerant pressure is sufficiently high above the valve member 12to hold the valve open. But, whenever the pressure in line 11 dropsappreciably below a predetermined acceptable value, the pressure belowthe valve member is sufficient to move the valve member 60 toward itsseat, thus to partially close or fully close the valve.

The closing of valve 12 tends to divert liquid refrigerant from line 11through the bypass circuit formed by line 26, the liquid circuit of unit6 and line 27. The fixed resistance to liquid flow in this bypass liquidcircuit is such that there is no refrigerant flow therethrough whenvalve 12 is open. However, as valve 12 is gradually closed, anincreasing portion of the liquid refrigerant is diverted through thebypass circuit. In the illustrative embodiment, when valve 12 isfullyclosed, there is a pressure drop of thirty pounds per square inchthrough this bypass liquid circuit.

During normal operation of the illustrative embodiment of the invention,with valve 12 open, the head pressure in the condenser is 140 pounds persquare inch. Valve 12 is adjusted to start closing whenever the pressurein line 11 drops below 120 pounds per square inch. With the valve fullyclosed so that there is a pressure drop of 30 pounds through the liquidbypass circuit, the effective head pressure in the receiver and at theexpansion valve is 90 poundsper square inch, i.e., the 120 poundspressure which is maintained in the condenser, minus the 30 pounds dropin the bypass circuit. During operation, with valve 12 partially orcompletely closed, the liquid refrigerant is heated by the hot gasrefrigerant, and an equilibrium condition is reached for any givencondition of operation, with suflicient liquid refrigerant beingsupplied to the evaporator. It should be noted that the heating of theliquid refrigerant by the heat interchange unit 6 is necessary tocompensate for the excessive subcooling of the refrigerant in thecondenser, and in that way the temperature of the liquid refrigerantfiowing to the receiver is raised to the value necessary to produce thedesired equilibrium condition in the receiver. Liquid refrigerant tendsto accumulate automatically in the lower portion of the condenser toreduce the effective condenser surface. That is, as liquid refrigerantaccumulates in the bottom of the condenser, only a reduced upper portionof the condenser is completely effective to condense refrigerant. Theliquid refrigerant is subco'oled in the condenser, but it is reheatedagain in unit 6. Simultaneously, the hot gas is cooled somewhat beforeit is passed to the condenser, and that reduces the temperature gradientbetween the refrigerant and the condensing medium so that there is areduced rate of heat transfer from the refrigerant in the condenser.Also, as indicated, the heating of the liquid refrigerant raises thetemperature and pressure in the receiver. Therefore, even though thetemperature of the condensercooling medium is very low, the pressuretends to build up.

The system of the present invention requires no manual or externalcontrol operation to cause the system to accommodate itself to changesin ambient temperatures.

The shifts from the normal mode of operation, with valve 12 open andwith a relatively high head pressure, to a condition where valve 12 ispartially or fully closed, and vice versa, take place without anyattention by the 3 operating personnel, and the system maintainssatisfactory performance at all times. The construction is not undulycomplicated, and the performance during normal operation is notpenalized by the presence of the unit 6 and valve 12.

' the form of the tube assemblies to produce the maximum desired heatingof the liquid refrigerant, and these tube assemblies provide someresistance to liquid flow while the remainder of such resistance isprovided by the orifice 56. Hence, unit 6 is designed to perform thedesired heat interchange functions and the desired resistance to liquidflow, and provides minimum resistance to gas flow. The illustrativepressures and operating conditions are for one particular installation,and other pressures and operating conditions will be encountered forother systems.

In the illustrative embodiment of the invention, unit 6 is positioned atthe outlet from the condenser, and it heats the refrigerant flowing tothe receiver. Under some circumstances, this unit may be positionedbetween the receiver and the expansion valve or other type of restrictorwhile still attaining certain of the advantages of the presentinvention. In such case, the liquid line extends to the bottom of thereceiver.

It has been indicated above that the present invention is applicable torefrigeration systems having evaporative condensers or even water-cooledcondensers equipped with cooling towers. For example, an evaporativecondenser is cooled with the aid of water evaporation during hotweather, and then cooled solely by air during cold weather, and theremay be excessive subcooling of the refrigerant during extremely coldweather. It will be understood that the present invention may beutilized to solve the.

problem of instability resulting from such excessive condenser cooling.

As many possible embodiments may be made of the steps of the method andthe mechanical features of the above invention herein described, allwithout departing from the scope of the invention, it is to beunderstood that all matter hereinabove set forth, or shown in theaccompanying drawings, is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. In a refrigeration system which includes, an evaporator andrestrictor means through which refrigerant flows to said evaporator anda condenser which tends to produce an excessively low head pressurewhereby insufiicient liquid refrigerant flows through said restrictormeans to said evaporator, the combination therewith of a normally openvalve positioned in the liquid refrigerant line between said condenserand said restrictor means and operative to close in response to -a dropin the head pressure below a predetermined value, and a refrigerantbypass circuit connected in parallel with said valve and havingsuflicient resistance to refrigerant flow to prevent any substantialflow therethrough when said valve is open, said bypass circuit includingmeans to heat the refrigerant flowing therethrough.

2. In a refrigeration system, the combination of, a compressor, an aircooled condenser, a receiver, a restrictor, an evaporator, a heatinterchange unit having a gas flow path through which refrigerant gasflows from the compressor and a liquid flow path through which theliquid refrigerant flows after leaving the condenser and before reachingthe restrictor, said liquid flow-path including means providingresistance to liquid flow, and a normally open valve connected inparallel with said liquid refrigerant flow path, said valve beingadapted to throttle the flow of liquid refrigerant through as it ismoved from its open position whereby refrigerant is diverted throughsaid liquid flow path and is heated by the hot refrigerant to saidexpansion valve.

3. A system as described in claim 2 which includes, means operative toclose said valve automatically in response to a drop in the pressure ofthe liquid refrigerant flowing from the condenser.

4. In a refrigeration system of the character described, the combinationof, a compressor, an evaporator, an aircooled condenser which is apt tobe subjected to low ambient temperatures whereby the refrigerantpressure therein is reduced to such a value that liquid refrigerant doesnot flow to said evaporator at a satisfactory rate, and means responsiveto a drop in said refrigerant pressure to pass refrigerant from saidcondenser into heat exchange relationship with refrigerant flowing fromsaid compressor, thereby to heat the liquid refrigerant and increase itspressure.

5. Apparatus as described in claim 8, wherein said lastnamed meanscomprises, a pair of gas heaters connected respectively to receive hotgas from said compressor and to deliver gas to said condenser, aplurality of tube assemblies mounted in said headers and each having apair of concentrically positioned tubes with an annular spacetherebetween open to said headers and having a fin assembly therein, theinner tube of each of said tube assemblies being connected in a liquidrefrigerant bypass circuit and having a fin assembly therein, and avalve connected in parallel with said bypass circuit and including meansresponsive to the pressure of the liquid refrigerant to open the valveat high refrigerant pressure and close the valve when the pressure dropswhereby liquid refrigerant is diverted through said bypass circuit bythe closing of said valve.

6. A system as described in claim 5, wherein said bypass circuitincludes orifice means constituting a restriction to the flow of liquidrefrigerant.

7. The method of maintaining stable operating conditions in arefrigeration system which includes a condenser to which refrigerantflows to be condensed and from which liquid refrigerant flows to anevaporator and which includes a restrictor in the path of flow from thecondenser and where there is a tendency for the refrigerant to flow tothe evaporator at an objectionably low rate when the head pressuredrops, the steps of, diverting refrigerant from its normal flow pathfrom the condenser to the restrictor along a secondary path toward saidrestrictor in response to a drop in head pressure, and heating theliquid refrigerant so diverted thereby to raise the head pressure.

8. In a refrigeration system which includes a compressor which deliversrefrigerant to a condenser and wherein there is a tendency for excessivecooling of refrigerant in the condenser to reduce the pressure of thecondensed refrigerant below a desired value, a heat interchange unitwhich is adapted to pass a stream of the refrigerant gas flowing fromthe compressor to the condenser into heat exchange relationship with therefrigerant liquid flowing from the condenser thereby to cool therefrigerant gas and to heat the refrigerant liquid, and means responsiveto a rise in the pressure of the condensed refrigerant to reduce therate of heat transfer within said heat interchange unit.

9. The method of maintaining stable operating conditions in arefrigeration system which includes a condenser to which refrigerantflows to be condensed and from which liquid refrigerant flows to anevaporator and which includes a restrictor in the path of flow from thecondenser and where there is a tendency for the refrigerant to flow tothe evaporator at an objectionably low rate when the head pressuredrops, the steps of, diverting refrigerant from its normal flow pathfrom the condenser to the restrictor along a secondary path toward saidrestrictor in response to a drop in head pressure, and heating theliquid refrigerant so diverted by passing it in heat exchangerelationship with hot gas refrigerant flowing toward the condenser.

References Cited in the file of this patent UNITED STATES PATENTS2,252,300 McGrath Aug. 12, 1941 2,404,112 Urban July 16, 1946 2,423,382Graham July 1, 1947 2,645,101 La Porte July 14, 1953 2,691,273 KramerOct. 12, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 2,956,419 October 18, 1960 Cecil Boling It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

line 55, for the claim reference numeral "8" Column 5,

line 56, for "heaters" read headers read 4 Signed and sealed this 19thday of December 1961 (SEAL) Attest: ERNEST W. SWIDER DAVID L. LADDCommissioner of Patents Attesting Officer USCOMM-DC

